Background: In a lamb model of brain injury an acute insult was
followed by a period of EEG depression which started after 10-20 minutes and
lasted for approximately 8 hours. After this seizures emerged, at around 10±3
hours (1). Even in the animal model there is wide variation in the duration of
insult which is required to produce an isoelectric EEG (2), and human babies are
not subjected to identical and reproducible insults. Despite this, we felt that
it would be interesting to examine the relationship between the EEG
determination of seizure onset time and our best estimate of the time of any
fetal/ neonatal insult in the human baby.

Aims: To establish whether or not the time of seizure onset, as
determined by EEG monitoring, was related to the time of the fetal/neonatal
cerebral insult (3). Previous work has examined the time of clinical seizure
onset, which is unreliable when compared to EEG.

Methods: Babies who were considered to be at high risk of seizure were
monitored prospectively using 12 channel continuous video-EEG telemetry, with
parental consent. The best estimate of the time of brain injury was determined
by careful review of the CTG traces, the obstetric history, and the peripartum
events by an observer (AD) who was blind to the EEG findings. In one case there
were neuropathological findings from autopsy.

Results: Eight babies with hypoxic-ischaemic encephalopathy had
monitoring commenced sufficiently early to allow detection of the time of first
electrographic seizure, and a further baby was already seizing when monitoring
began (at 5 hours). In 3 babies it was thought that the insult had occurred
before labour and more than 12 hours before birth. In this group the EEG seizure
onset time was 4, 5.5 and 9.5 hours respectively. These babies began seizing
earlier than the 6 whose insult was thought to have occurred during labour or
close to the time of birth. In these babies the first seizure was detected at
11.5, 12, 13, 18, 20 and 26 hours after birth. This gave a median seizure onset
time of 15.5 hours compared to 5.5 hours (Mann Whitney P value=0.02).

Conclusion: Babies who had suffered an acute hypoxic-ischaemic insult
close to birth had their first EEG seizure later than those whose history
suggested that their brain injury was sustained before labour began. The EEG in
this group followed a very similar pattern to that seen in the lamb model after
an acute insult. Our results suggest that babies with EEG seizure onset at less
than 6 hours probably did not sustain their brain injury at around the time of
birth. Continuous EEG monitoring from birth may allow a more precise estimate of
the time of brain injury to be made than that which is currently possible with
other methods.